1. Field of the Invention
The invention relates to a dynamic power equalizer, and especially to a dynamic power equalizer having double-loop array wave-guide gratings.
2. Related Art
The trend of optical wave communication systems of the next generation is toward the development and enhancement of the technologies of Dense Wavelength-Division Multiplexing (hereinafter abbreviated and referred to as DWDM) and Dynamic Add/Drop. In this dynamic DWDM communication system, the system manager is capable of taking out or adding in signals of the required wavelength at the pertinent node, or altering the communication channel of any wavelength depending on the actual requirements. As such, the frequency number of the components of the optical signal entering the optical fiber amplifier at the relay node is no longer a fixed number, thus the variation of the power intensity of the input signal causes variation of the gain vs. frequency relations of the optical fiber amplifier, which in turn causes variation of the originally smooth and even gain vs. frequency relations of the DWDM communication system, thus resulting in the increase of distortion and erroneous coding rate. Therefore, the design and development of the dynamic power equalizer that is capable of accommodating the input signals of dynamically varying frequency ranges is the most important task for the designer of the DWDM communication system.
Presently, the technology employed in manufacturing the dynamic power equalizer mainly involves manufacturing the dynamic power equalizer module through the combination of conventional optical elements and components of the optical power adjustment mechanism by means of hybrid packaging. For example, the cascaded multi-stage liquid crystal birefringent filter disclosed in U.S. Pat. No. 6,429,962 is utilized to produce an optical power adjustment mechanism having optical wave filtering functions. In addition, the see-saw array is made by means of the Micro Electro-Mechanical System (MEMS) as disclosed in U.S. Pat. No. 6,556,766 to match and cooperate with the optical power adjustment mechanism having optical wave filtering functions. The assembly and packaging of the above-mentioned dynamic power equalizer module is realized by making use of the traditional components of the lens and optical crystal, etc. As such, it is quite bulky, thus having high assembly and packaging cost, and it is not feasible for mass production.
For more detailed description of the conventional optical power equalizer, please refer to FIG. 1. As shown in FIG. 1, the dynamic power equalizer having the array waveguide grating 100 as disclosed in JP 07-98424 is provided with a plurality of input wave guides 110,120 at one end, and a corresponding plurality of output waveguides 130,140 at the other end. Although the structure of its constituting loops is relatively simple, the lead in and lead out of its optical signals is prone to be misguided into different loops. For example, when the optical signal is guided in through one end of the input wave-guide of the array waveguide grating 100, it should be led out from wave guide 130 after being processed by the array waveguide grating 100. However, in actuality, some of the optical signals may be output from the output waveguide 140, and thus its operation stability is unsatisfactory.